Marginocephalia Lecture 13 PDF

LECTURE 13: Marginocephalia From Chapter 11; Chapter 6, p. 140-141 of Dinosaurs (4th Ed.  LECTURE 13: Marginocephalia From Chapter 11; Chapter 6, p. 140-141 of Dinosaurs (4th Ed. Outline Introduction to Marginocephalia  LECTURE 13: Margino...

LECTURE 13: Marginocephalia From Chapter 11; Chapter 6, p. 140-141 of Dinosaurs (4th Ed.  LECTURE 13: Marginocephalia From Chapter 11; Chapter 6, p. 140-141 of Dinosaurs (4th Ed. Outline Introduction to Marginocephalia  LECTURE 13: Marginocephalia From Chapter 11; Chapter 6, p. 140-141 of Dinosaurs (4th Ed. Objectives Understand the evolution of Marginocephalia and the clades Pachycephalosauria & Ceratopsia Develop an understanding of the current thinking about the lifestyles and behaviours of marginocephalians Ornithischia: Neornithischia Basal Ornithomimosaur Neornithischia = Basal neornithischians + Cerapoda Neornithischia:Basal Cerapoda Ornithomimosaur Cerapoda = Marginocephalia + Iguanodons Ornithopoda Pachycephalosaurs Ceratopsians Hadrosaurs Key Characters (synapomorphies) 1. Gap between teeth of the maxilla and premaxilla (1) 1 2. ≤ 5 premaxillary teeth (2) 2 Hypsilophodon Image: Cerapoda: Marginocephalia Basal Ornithomimosaur Marginocephalia = Ceratopsia + Pachycephalosauria Key Marginocephalia character (synapomorphy): A bony shelf around back of skull that blocks the view of occiput Stegoce ras Protocerat Cerapoda: Marginocephalia Basal Ornithomimosaur Marginocephalia = Ceratopsia + Pachycephalosauria Key Marginocephalia character (synapomorphy): A bony shelf around back of skull that blocks the view of occiput Stegoce ras Protocerat  Cerapoda: Marginocephalia Oldest marginocephalian is Yinling (basal Courtesy Tom Holtz Marginocephalia: Pachycephalosauria Basal Ornithomimosaur Marginocephalia: Pachycephalosauria Basal Ornithomimosaur pachy – thick; cephal – head ("thick headed lizards") Key Characters (synapomorphies): 1 Thickened skull roof (1) Osteoderms on 2 squamosal (2) Prenocephale Dracorex FASTOVSKY Fig. 11.15 © Cambridge University Pachycephalosauria: Body Shape Homalocephale, L. Cret, Mongolia Distinctive thickening of skull roof 2 to 7 m in length Very wide-bodied anterior to the pelvis Bipedal; three-toed print; four toes Image: Scott Hartman Stegoceras, L. Cret, Alberta  Pachycephalosauria: Skulls Pachycephalosaurus, L. Cret., USA mocephale, L. Cret., Mongolia Variably between species: Thickened skull roof Domed or flattened Enlarged olfactory lobes nocephale, L. Cret., Mongolia Tylocephale, L. Cret., Mongolia Stegoceras, L. Cret., Alberta Prenocephale  Pachycephalosauria: Skulls All have beaks at front of jaw Inset tooth row Well-developed coronoid process Premaxillary teeth > in more basal forms Knobs and hornlets around base of dome (episquamosals & venile Pachycephalosaurus (“Dracorex”), epiparietal Late Cretaceous, Western USA ornamentation)  Pachycephalosauria Pachycephalosaurus, L. Cret., USA mocephale, L. Cret., Mongolia nocephale, L. Cret., Mongolia Tylocephale, L. Cret., Mongolia Skull caps are the most common Stegoceras, L. Cret., Alberta pachycephalosaur fossil  Where Are All The Pachycephalosaurs? Why are pachycephalosaur skeletons so rare? Did they live in upland environments where skeletons had less chance to fossilize? Or are small-bodied animals just less likely to be preserved?  Where Are All The Pachycephalosaurs? Why are pachycephalosaur skeletons so rare? Did they live in upland environments where skeletons had less chance to fossilize? Or are small-bodied animals just less likely to be preserved? Where Are All The Pachycephalosaurs?  Pachycephalosauria: Lifestyle Poorly known herbivores of late Mesozoic (complete skeletons rare) Low browser: Food consumption combined chewing and gastric breakdown Domes for intraspecific behaviors (display) and likely combat No evidence for other social behavior as fossils are not common Acrotholus audeti, Milk River Formation, Late Cretaceous, Alberta  Pachycephalosauria: Skulls Stegoceras headbutting Skull occiput has large muscle attachment sites Skull bone fibers run vertically, suggesting that the strongest resistance to impact in the skull is vertical This suggest that the pachycephalosaur skull is designed for impacts at the top of the head  Pachycephalosauria: Ontogeny Ontogeny in Pachycephalosaurus, Late Cret., Hell Creek Fm, US Pachycephalosauru Adult ‘Stygimoloch’ Subadult ‘Dracorex’ Juvenile Images: Creative  Pachycephalosauria: Ontogeny Development of the Dome Growth series of Stegoceras validum in dorsal (top) and lateral (bottom) views Note transition from a flat-headed to domed frontoparietal Marginocephalia: Ceratopsia Basal Ornithomimosaur Marginocephalia: Ceratopsia Basal Ornithomimosaur Ceratopsia: Cera – horn; tops – face Basalmost forms were bipedal Derived forms quadrupedal, large Geographic range – NA & Asia Late Jurassic to latest Cretaceous Psittacosaurus, Early Cret., Asia Albertaceratops, Late Cret., Albert  Ceratopsia Basal Ornithomimosaur Key Characters (synapomorphies) Rostral (forms upper half of beak) Jugal horn Triceratop rostral Jugal horn FASTOVSKY Fig. 11.19 Psittacosaurus dorsal view  Ceratopsia: Psittacosauridae Basal Ornithomimosaur tacosaurus, Early Cretaceous, Asia Short, deep skull; short tail Adults bipedal; hatchlings probably quadrupedal Tails have ‘quills’ Bonebed accumulations suggest social (parental?) behaviour  Basal Ceratopsia: Yinlong Basal Ornithomimosaur g downsi - a basal ceratopsian ate Jurassic of China al (1) larger than most ornithischians but < other ceratopsians ened jugal, but no flange (2) ted post skull, but no parietal contribution to frill (3) 3 dal; forelimbs 100,000 elements preserved from 100s or Images: M Ryan Skeletons: Scott hartman  Ceratopsia: Palaeobiogeography Laying the ceratopsian cladogram over a map, it is clear that the most basal forms are located in Asia; more derived forms are in North America. This strongly suggests that the migration went from Asia  North  EVOLUTIONARY PATTERNS IN MARGINOCEPHALIA 1. Feeding Pachycephalosaurs have relatively unspecialized snouts and teeth, and so were probably nipping browsers Basal ceratopsians increased their jaw power and evolved the cropping rostral bone (+ predentary = ‘beak’) The frill of basal ceratopsians greatly increased their jaw muscle power Shearing dental batteries in Ceratopsidae gave them one of the most powerful bites to evolve among amniotes  EVOLUTIONARY PATTERNS IN MARGINOCEPHALIA 2. Locomotion  Pachycephalosaurs, basal ceratopsians, and basal neoceratopsians were bipedal  Increased skull size forced advanced neoceratopsians onto all fours, such that coronosaurs were obligate quadrupeds  EVOLUTIONARY PATTERNS IN MARGINOCEPHALIA 3. Size Trends  Most pachycephalosaurs, basal ceratopsians, and basal neoceratopsians were small (all in the 1-3 m range)  Increased size in pachycephalosaurs (e.g., Pachycepahlosaurus) only occurs at the very end of the Late Cretaceous.  For most of its history, Ceratopsia consisted of only small dinosaurs  Advanced neoceratopsians show a size increase earlier than pachycephalosaurs, culminating in the major size increases at the base of Ceratopsoidea Ceratopsia: Body Size & Jaws Small size 10 to 100 kg Simple teeth Ceratopsia: Body Size & Jaws Large size 100 to 1000+ kg 10 to 100 kg Complex tooth battery  EVOLUTIONARY PATTERNS IN MARGINOCEPHALIA 4. Social Behaviour  Both pachycephalosaurs and ceratopsians probably used their heads for within-species interactions.  Ornamentation (marginal osteoderms, domes, frills, horns, etc.) and possible combat features (thickened skulls, horns) are present in both clades, but typically only in at full adult size.  Evidence for gregarious behaviour is present throughout Ceratopsia